EPSC 2013: Don Quixote revealed as a comet hiding in plain sight

For 30 years, a large near-Earth asteroid wandered its lone, intrepid path, passing before the scrutinizing eyes of scientists while keeping something to itself: (3552) Don Quixote, whose journey stretches to the orbit of Jupiter, now appears to be a comet. The finding will be presented by Dr Michael Mommert at the European Planetary Science Congress (EPSC) 2013 in London on Tuesday 10 September.

The discovery resulted from an ongoing project coordinated by researchers at Northern Arizona University using the Spitzer Space Telescope. Through a lot of focused attention and a little bit of luck, they found evidence of cometary activity that had evaded detection for three decades.

“Don Quixote’s orbit resembles that of a comet, so people assumed it was a comet that had gotten rid of all its ice deposits thousands of years ago,” said Mommert, a PhD student of team member Prof. Alan Harris at the German Aerospace Center (DLR) in Berlin at the time this work was carried out. Near-Earth asteroids that are former comets make up roughly 5 percent of the whole near-Earth asteroid population, as found by Mommert and colleagues in a related study. These objects are mostly “dead comets” – comets that had shed the carbon dioxide and water that give them their spectacular comae and tails long time ago.

What Mommert, now a post-doctoral researcher at NAU, and an international team of researchers discovered, though, was that Don Quixote was not actually a dead comet. In fact, the third-biggest near-Earth asteroid out there, skirting Earth with an erratic, extended orbit, is “sopping wet,” said NAU associate professor David Trilling, with large deposits of carbon dioxide and presumably water ice.

Finding evidence of carbon dioxide wasn’t easy. During an observation of the object using Spitzer in August 2009, Mommert and colleagues found that it was far brighter than they expected. “The images were not as clean as we would like, so we set them aside,” Trilling said.

Much later, though, Mommert prompted a closer look, and partners at the Harvard-Smithsonian Center for Astrophysics found something unusual when comparing the infrared images of the object: something, that is, where an asteroid would have shown nothing. The processed images indicated that Don Quixote had a coma and a faint tail.

“This discovery of carbon dioxide emission from Don Quixote required the sensitivity and infrared wavelengths of the Spitzer telescope and would not have been possible using optical telescopes on the ground,” Mommert said. This discovery implies that carbon dioxide and water ice might be present on other near-Earth asteroids, as well.

The implications have less to do with a potential impact, which is extremely unlikely in this case, and more with “the origins of water on Earth,” Trilling said. Comets may be the source of at least some of it, and the amount on Don Quixote represents about 100 billion tons of water—roughly the same amount that can be found in Lake Tahoe, California.

This study has confirmed Don Quixote’s size and the low, comet-like reflectivity of its surface. The results of this study have been submitted to the Astrophysical Journal for publication. Michael Mommert’s work at the DLR’s Institute of Planetary Research in Berlin was funded by Grant HA 2914/2-2 from the German Research Foundation (DFG).

With the help of NASA’s Spitzer Space Telescope, astronomers have discovered that what was thought to be a large asteroid called Don Quixote is in fact a comet.

The left image shows Don Quixote’s coma and tail — features of comets — as seen in infrared light by Spitzer. The coma appears as a faint glow around the center of the body, caused by dust and gas. The tail, which appears more clearly in the right image, points towards the right-hand side of Don Quixote, into the direction opposite of the sun.

The right image represents a more elaborate image processing step, in which the glow of the coma has been removed based on a model comet coma. Bright speckles around Don Quixote are background stars; the horizontal bar covers image artifacts caused by the image processing.

EPSC is the major European meeting on planetary science. EPSC 2013 is taking place at University College London (UCL) from Sunday 8 September to Friday 13 September 2013. It is the first time that the Congress has been held in the UK. The 2013 programme includes around 75 sessions and workshops. Details of the Congress and a full schedule of EPSC 2013 scientific sessions and events can be found at the official website: http://www.epsc2013.eu/

EPSC 2013 is organised by Europlanet, UCL and Copernicus Meetings and the event is sponsored by the UK Space Agency, UCL, Astrium and the Science and Technology Facilities Council.

To celebrate EPSC coming to London, a ‘Festival of the Planets’ has been organised across the Capital in collaboration with partners including the Baker Street Irregular Astronomers, the Bloomsbury Theatre, the British Astronomical Association, the British Interplanetary Society, the Natural History Museum, the Open University, Queen Mary University of London, the Royal Astronomical Society, Royal Museums Greenwich and University College London. More information about the events can be found at: http://www.europlanet-eu.org/epsc2013/outreach-activities

Follow #epsc2013 @epsc2013 @europlanetmedia on Twitter

About Europlanet Europlanet is a network of planetary scientists, whose aim is to bring together the disparate European community so that Europe can play a leading role in space exploration. Europlanet’s activities complement the mission activities of the European Space Agency through field work at planetary-analogue terrains on Earth, laboratory measurements, computer modelling and observations from ground-based telescopes. Founded in 2002 and funded by the European Commission from 2005-2012, Europlanet has evolved into a community-based organisation that will carry on this work and plan for future missions and mission support.

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.

We are among the world’s top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world. UCL has nearly 27,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses – UCL Australia and UCL Qatar. Our annual income is more than £800 million. www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel YouTube.com/UCLTV

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 654208.